Communication terminal apparatus, base station apparatus, and radio communication method

ABSTRACT

A communication mode determination section  201  determines the communication mode based on the CIR measured by a CIR measurement section  219 ; a DRC signal creation section  202  creates a DRC signal with a number corresponding to the communication mode; and a DRC power controller  205  refers to a transmission power table  206  showing the correspondence between DRC numbers and transmission power, and, based on the transmission power of the pilot signal output from a pilot power controller  209 , increases transmission power in proportion as the DRC signal indicates that downlink channel quality is good.

This application is a 371 of PCT/JP01/0665 Aug. 8, 2001.

TECHNICAL FIELD

The present invention relates to a communication terminal apparatus,base station apparatus, and radio communication method to be used in acellular communication system.

BACKGROUND ART

In a cellular communication system, one base station performs radiocommunication with a plurality of communication terminalssimultaneously, and therefore, as demand has increased in recent years,so has the need for higher transmission efficiency.

One technology that has been proposed for increasing the transmissionefficiency of a downlink from a base station to a communication terminalis HDR (High Data Rate). HDR is a communication method whereby a basestation performs scheduling for allocating communication resources tocommunication terminals by time division, and also sets a transmissionrate for each communication terminal according to the downlink channelquality.

The operations by which a base station and communication terminalsperform radio communication with HDR are described below. First, thebase station transmits a pilot signal to each communication terminal.Each communication terminal estimates the downlink channel quality usinga CIR (desired carrier to interference ratio) based on the pilot signal,etc., and finds a transmission rate at which communication is possible.Then, based on the transmission rate at which communication is possible,each communication terminal selects a communication mode, which is acombination of packet length, coding method, and modulation method, andtransmits a data rate control (hereinafter referred to as “DRC”) signalindicating the communication mode to the base station.

The type of modulation method that can be used in each system ispredetermined as BPSK, QPSK, 16 QAM, 64 QAM, and so forth. Also, thetype of coding that can be used in each system is predetermined as ½turbo code, ⅓ turbo code, ¾ turbo code, and so forth. Further, aplurality of transmission rates that can be used in each system arepredetermined according to a combination of packet length, modulationmethod, and coding method. Each communication terminal selects acombination whereby communication can be performed most efficiently withthe current downlink channel quality, and transmits a DRC signalindicating the selected communication mode to the base station.Generally, DRC signals are represented by numbers from 1 to N, with ahigher number indicating a proportionally better downlink channelquality.

Based on the DRC signal transmitted from each communication terminal,the base station sets a transmission rate for each communicationterminal, and sends a signal to each communication terminal via acontrol channel indicating communication resource allocation to eachcommunication terminal. Generally, taking improvement of systemtransmission efficiency into consideration, communication resources areallocated with priority to the communication terminal that has the bestdownlink channel quality-that is to say, the communication terminal thattransmits the highest-numbered DRC signal.

The base station then transmits data only to the relevant communicationterminal in its allocated time. For example, if time t1 has beenallocated to communication terminal A, in time t1 the base stationtransmits data only to communication terminal A, and does not transmitdata to a communication terminal other than communication terminal A.

In this way, data transmission efficiency has conventionally beenincreased for the overall system by setting a transmission rate for eachcommunication terminal according to channel quality by means of HDR, andperforming communication resource allocation with priority to acommunication terminal with a high transmission rate at whichcommunication is possible.

However, if the communication mode determined by a communicationterminal is received erroneously by the base station due todeterioration of the channel conditions on the uplink from thecommunication terminal to the base station, or the like, the basestation will transmit data using that erroneous mode. As the determinedcommunication mode and the communication mode of data transmitted to thecommunication terminal are different, the communication terminal cannotdemodulate or decode the data.

Also, when a base station such as that described above has allocatedtime t1 to communication terminal A, in time t1 the base stationtransmits data only to communication terminal A, and does not transmitdata to a communication terminal other than communication terminal A.

Due to the above, a problem arises in that, if the communication modedetermined by a communication terminal is received erroneously by thebase station, there will be an interval during which time-dividedcommunication resources are not used, and downlink throughput falls.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a communicationterminal apparatus, base station apparatus, and radio communicationmethod that make it possible to prevent a fall in downlink throughput ina communication system in which communication resources are allocated tocommunication terminals based on downlink channel quality.

In order to achieve the above-described object, in the presentinvention, with respect to information, among information indicative ofdownlink channel quality, which has a possibility of decreasing thedownlink throughput when the information is received erroneously in abase station, a communication terminal provides such information withless susceptibility to errors in the propagation path to transmit. It isthereby possible to prevent the downlink throughput from decreasing.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 a graph illustrating DRC signal selection frequency in a basestation;

FIG. 2 is a block diagram showing a configuration of a base stationaccording to Embodiment 1 of the present invention;

FIG. 3 is a block diagram showing the configuration of a communicationterminal according to Embodiment 1 of the present invention;

FIG. 4 is a drawing showing the contents of the transmission power tableprovided in a communication terminal according to Embodiment 1 of thepresent invention;

FIG. 5 is a block diagram showing another configuration of a basestation according to Embodiment 1 of the present invention;

FIG. 6 is a block diagram showing the configuration of a communicationterminal according to Embodiment 2 of the present invention;

FIG. 7 is a drawing showing the contents of the code word table providedin a communication terminal according to Embodiment 2 of the presentinvention;

FIG. 8 is a block diagram showing the configuration of a base stationaccording to Embodiment 3 of the present invention;

FIG. 9 is a block diagram showing the configuration of a communicationterminal according to Embodiment 3 of the present invention;

FIG. 10 is a block diagram showing a configuration of a base stationaccording to Embodiment 4 of the present invention;

FIG. 11 is a block diagram showing the configuration of a communicationterminal according to Embodiment 4 of the present invention;

FIG. 12 is a block diagram showing another configuration of a basestation according to Embodiment 4 of the present invention;

FIG. 13 is a block diagram showing the configuration of a communicationterminal according to Embodiment 5 of the present invention;

FIG. 14 is a block diagram showing the configuration of a communicationterminal according to Embodiment 6 of the present invention;

FIG. 15 is a block diagram showing the configuration of the CIR signalcreation section of a communication terminal according to Embodiment 6of the present invention;

FIG. 16 is a block diagram showing the configuration of the CIR signalcreation section of a communication terminal according to Embodiment 7of the present invention; and

FIG. 17 is a block diagram showing the configuration of the CIR signalcreation section of a communication terminal according to Embodiment 8of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

With reference now to the accompanying drawings, embodiments of thepresent invention will be explained in detail below.

Embodiment 1

As stated above, a base station allocates communication resources withpriority to the communication terminal with the best downlink channelquality. In other words, a base station selects the highest-numbered DRCsignal, and allocates communication resources with priority to thecommunication terminal that transmitted that selected DRC signal. Thus,DRC signal selection frequency is as shown in FIG. 1. FIG. 1 is a graphillustrating DRC signal selection frequency in a base station. In thisfigure, numbers 1 to 5 are used as DRC numbers, with a higher numberrepresenting a proportionally better channel quality.

As shown in FIG. 1, the higher the number of a DRC signal, the greateris the frequency of its selection by the base station. That is to say,the better the downlink channel quality of a communication terminal, thehigher is the frequency with which communication resources are allocatedto that communication terminal. This kind of relationship arises fromthe fact that there are many communication terminals, and there is anincreased probability of there being a communication terminal with gooddownlink channel quality.

Thus, the selection frequency of each DRC signal differs according tochannel quality. That is to say, since a DRC signal indicating thatdownlink channel quality is good tends to be selected with greaterfrequency, there is a high probability that downlink throughput willfall if a DRC signal indicating that downlink channel quality is good isreceived erroneously. Also, since a DRC signal indicating that downlinkchannel quality is poor tends to be selected with lower frequency, thereis little effect of producing a fall in downlink throughput if a DRCsignal indicating that downlink channel quality is poor is receivederroneously.

Thus, a communication terminal according to Embodiment 1 of the presentinvention transmits at proportionally higher transmission power a DRCsignal indicating that downlink channel quality is good. Also, a basestation according to Embodiment 1 of the present invention excludes DRCsignals with reception power lower than a predetermined threshold valuein performing communication resource allocation.

FIG. 2 is a block diagram showing a configuration of a base stationaccording to Embodiment 1 of the present invention.

In FIG. 2, an allocation section 101 determines communication resourceallocation to each communication terminal based on DRC signals excludingDRC signals detected by unused DRC detection sections 116 describedlater herein from among DRC signals extracted by demodulators 114described later herein. Then, based on the determined communicationresource allocation, the allocation section 101 notifies a buffer 102for output of downlink transmit data, indicates the downlink transmitdata coding method to an adaptive coding section 103, and indicates thedownlink transmit data modulation method to an adaptive modulator 104.

The buffer 102 holds downlink transmit data, and outputs downlinktransmit data for a predetermined communication terminal to the adaptivecoding section 103 in accordance with the directions of the allocationsection 101. The adaptive coding section 103 codes the output signalfrom the buffer 102 in accordance with the directions of the allocationsection 101, and outputs the resulting signal to the adaptive modulator104. The adaptive modulator 104 modulates the output signal from theadaptive coding section 103 in accordance with the directions of theallocation section 101, and outputs the resulting signal to a spreadingsection 105. Spreading section 105 spreads the output signal from theadaptive modulator 104, and outputs the resulting signal to amultiplexer 108.

Amodulator 106 modulates a pilot signal and outputs it to a spreadingsection 107. Spreading section 107 spreads the output signal from themodulator 106, and outputs the resulting signal to the multiplexer 108.

The multiplexer 108 performs time multiplexing of the spread pilotsignal with the spread downlink transmit data at predeterminedintervals, and outputs the resulting signal to a transmit RF section109. The transmit RF section 109 converts the frequency of the outputsignal from the multiplexer 108 to radio frequency, and outputs theresulting signal to a duplexer 110.

The duplexer 110 transmits the output signal from the transmit RFsection 109 as a radio signal from an antenna 111 to a communicationterminal. Moreover, the duplexer 110 outputs the signals transmittedfrom each communication terminal and received by antenna 111 to receiveRF section 112.

A receive RF section 112 converts the frequency of a radio frequencysignal output from the duplexer 110 to baseband, and outputs theresulting signal to a despreading section 113. The despreading section113 despreads the baseband signal using the spreading code used tospread the DRC signal, and outputs the resulting signal to thedemodulator 114 and a reception power calculation section 115.

The demodulator 114 demodulates the output signal from the despreadingsection 113 and extracts the DRC signal, and outputs this signal to theallocation section 101.

The reception power calculation section 115 measures the reception powerof the despread DRC signal, which is output to the unused DRC detectionsection 116. In the unused DRC detection section 116 is set apredetermined threshold value, as described later herein, and a DRCsignal of reception power lower than this threshold value is detected,and the result of the detection is output to the allocation section 101.

A despreading section 113, demodulator 114, reception power calculationsection 115, and unused DRC detection section 116 are provided for eachcommunication terminal. From each demodulator 114 a DRC signal for thecorresponding communication terminal is output, and from each unused DRCdetection section 116 a detection result for the correspondingcommunication terminal is output.

FIG. 3 is a block diagram showing the configuration of a communicationterminal according to Embodiment 1 of the present invention. In FIG. 3,a communication mode determination section 201 determines acommunication mode indicating a combination of modulation method andcoding method based on a CIR measured by a CIR measurement section 219described later herein, and outputs the result to a DRC signal creationsection 202. The communication mode determination section 201 alsoindicates the downlink receive data demodulation method to an adaptivedemodulator 216, and indicates the downlink receive data decoding methodto an adaptive decoding section 217, based on the determinedcommunication mode.

The DRC signal creation section 202 creates a DRC signal with a numbercorresponding to the communication mode output from the communicationmode determination section 201, and outputs this DRC signal to amodulator 203 and DRC power controller 205.

Modulator 203 modulates the DRC signal and outputs the resulting signalto a spreading section 204. Spreading section 204 spreads the outputsignal from modulator 203 and outputs the resulting signal to the DRCpower controller 205. The DRC power controller 205 refers to atransmission power table 206 that shows the correspondence between DRCnumbers and transmission power, controls the DRC signal transmissionpower based on the transmission power of a pilot signal output from apilot power controller 209 described later herein, and outputs the DRCsignal that has undergone transmission power control to a multiplexer210. The actual method of controlling DRC signal transmission power willbe described later herein.

A modulator 207 modulates the pilot signal and outputs the resultingsignal to a spreading section 208. Spreading section 208 spreads theoutput signal from modulator 207 and outputs the resulting signal to thepilot power controller 209. The pilot power controller 209 controls thetransmission power of the pilot signal, and outputs the pilot signalthat has undergone transmission power control to the multiplexer 210.The pilot power controller 209 also outputs the pilot signaltransmission power to the DRC power controller 205.

The multiplexer 210 performs time multiplexing of the DRC signal thathas undergone transmission power control and the pilot signal that hasundergone transmission power control at predetermined intervals, andoutputs the resulting signal to a transmit RF section 211. The transmitRF section 211 converts the frequency of the output signal from themultiplexer 210 to radio frequency, and outputs the resulting signal toa duplexer 212.

The duplexer 212 transmits the output signal from the transmit RFsection 211 as a radio signal from an antenna 213 to the base station.Also, a signal transmitted as a radio signal by the base station andreceived as a radio signal by the antenna 213 is output by the duplexer212 to a receive RF section 214.

The receive RF section 214 converts the frequency of the radio frequencysignal output from the duplexer 212 to baseband, and outputs theresulting signal to a despreading section 215 and a despreading section218.

Despreading section 215 despreads the data component of the basebandsignal and outputs the resulting signal to the adaptive demodulator 216.The adaptive demodulator 216 demodulates the output signal fromdespreading section 215 in accordance with the directions of thecommunication mode determination section 201, and outputs the resultingsignal to the adaptive decoding section 217. The adaptive decodingsection 217 decodes the output signal from the adaptive demodulator 216in accordance with the directions of the communication modedetermination section 201, and obtains receive data.

Despreading section 218 despreads the pilot signal component of thebaseband signal and outputs the resulting signal to a CIR measurementsection 219. The CIR measurement section 219 measures the CIR of thepilot signal output from despreading section 218, and outputs the resultto the communication mode determination section 201.

Next, the procedure for transmission/reception of signals between thebase station shown in FIG. 2 and the communication terminal shown inFIG. 3 will be described.

First, at the start of communication, a pilot signal is modulated by themodulator 106 in the base station, is spread by spreading section 107,and is output to the multiplexer 108. Only the spread pilot signal isoutput from the multiplexer 108 to the transmit RF section 109. Thespread pilot signal is frequency-converted to radio frequency by thetransmit RF section 109, and transmitted to communication terminals as aradio signal from the antenna 111 via the duplexer 110.

A radio signal of only the pilot signal component transmitted as a radiosignal from the base station is received by the antenna 213 of thecommunication terminal, passes through the duplexer 212, and isfrequency-converted to baseband by the receive RF section 214. The pilotsignal component of the baseband signal is despread by despreadingsection 218, and output to the CIR measurement section 219.

Next, in the CIR measurement section 219, the CIR of the pilot signaloutput from despreading section 218 is measured, and based on the CIR,the communication mode is determined by the communication modedetermination section 201. Then a DRC signal with a number correspondingto the communication mode is created by the DRC signal creation section202.

The DRC signal is modulated by modulator 203, spread by spreadingsection 204, and output to the DRC power controller 205. In the DRCpower controller 205, the DRC signal transmission power is controlledbased on the transmission power of the pilot signal output from thepilot power controller 209, and the ratios of pilot signal transmissionpower to DRC signal transmission power set beforehand in thetransmission power table 206.

The contents set in the transmission power table 206 will be describedbelow. FIG. 4 is a drawing showing the contents of the transmissionpower table provided in a communication terminal according to Embodiment1 of the present invention.

The transmission power table 206 shows the correspondence between DRCnumbers and DRC signal transmission power, set so that the higher theDRC number, the higher is the transmission power. Here, numbers 1 to 5are used as DRC numbers, with a higher number representing aproportionally better downlink channel quality. That is to say, in thesettings in the transmission power table 206, the better the downlinkchannel quality indicated by a DRC signal, the higher is thetransmission power.

As explained above, the frequency of selection by the base station tendsto be proportional to the downlink channel quality indicated by a DRCsignal, and therefore in this embodiment, transmission power is higher,and susceptibility to errors lower, the better the downlink channelquality indicated by a DRC signal. As a result, the probability of a DRCsignal that indicates that downlink channel quality is good beingreceived erroneously can be made lower than the probability of a DRCsignal that indicates that downlink channel quality is poor beingreceived erroneously. In other words, the probability of a DRC signalwith a high frequency of selection by the base station being receivederroneously can be made lower than the probability of a DRC signal witha low frequency of selection by the base station being receivederroneously.

The DRC signal transmission power values set in the transmission powertable 206 are expressed as a ratio to the pilot signal transmissionpower. Here, as shown in FIG. 4, the settings are arranged so that DRCnumber 3 in the middle of DRC numbers 1 to 5 is taken as a reference,and DRC signals indicating a lower number than DRC number 3 aretransmitted at lower transmission power than the pilot signaltransmission power, while DRC signals indicating a higher number thanDRC number 3 are transmitted at higher transmission power than the pilotsignal transmission power. That is to say, the settings are arranged sothat DRC signals indicating a poorer channel quality than apredetermined channel quality (here, the channel quality correspondingto a DRC signal with DRC number 3) are transmitted at lower transmissionpower than the pilot signal transmission power, while DRC signalsindicating a better channel quality than the predetermined channelquality are transmitted at higher transmission power than the pilotsignal transmission power.

Thus, with this embodiment, by setting DRC signals for whichtransmission power is increased and DRC signals for which transmissionpower is decreased in comparison with conventional DRC signaltransmission power (here, that is, pilot signal transmission power), andmaking the total of DRC signal transmission power increases anddecreases ±0 dB, it is possible to make DRC signals indicating thatdownlink channel quality is good proportionally less susceptible toerrors while keeping average DRC signal transmission power constantcompared with a conventional system. That is to say, it is possible toproportionally reduce susceptibility to errors of DRC signals indicatingthat downlink channel quality is good without reducing uplink capacitycompared with a conventional system.

Also, since, in this way, DRC signals indicating that downlink channelquality is poor (DRC signals with DRC numbers 1 and 2 in FIG. 4) aretransmitted at lower transmission power than in a conventional system,it is possible to reduce power consumption in a communication terminalthat is located far from the base station and for which there is a highprobability of transmitting a DRC signal indicating that downlinkchannel quality is poor. That is to say, in the case of a communicationterminal that transmits a DRC signal indicating that downlink channelquality is poor, whereas the DRC signal was previously transmitted attransmission power that was high to begin with, according to thisembodiment the DRC signal transmission power can be made lower than thathigh transmission power, enabling communication terminal powerconsumption to be greatly reduced.

As the frequency of selection by a base station is low to begin with fora DRC signal indicating that downlink channel quality is poor, there isalmost no effect of producing a fall in throughput due to transmitting aDRC signal indicating that downlink channel quality is poor at lowertransmission power than previously in this way.

Also, with this embodiment, DRC signals indicating that uplink channelquality is good (DRC signals with DRC numbers 4 and 5 in FIG. 4) aretransmitted at higher transmission power than in a conventional system.However, there is a high possibility of a DRC signal indicating thatuplink channel quality is good being transmitted from a communicationterminal located comparatively near the base station. Also, due to pilotsignal transmission power control that is performed constantly on anuplink, the transmission power of a pilot signal transmitted from acommunication terminal located comparatively near the base station (thatis, the conventional DRC signal transmission power) is low to beginwith. Therefore, in the case of a communication terminal that transmitsa DRC signal indicating that uplink channel quality is good, DRC signaltransmission power remains low and power consumption remains low eventhough the previously originally low DRC signal transmission powerincreases, and so there is almost no effect on power consumption.

In the DRC power controller 205, the DRC signal transmission power isobtained by having the transmission power of the pilot signal outputfrom the pilot power controller 209 adjusted in accordance with theratios set in the transmission power table 206. Then, in the DRC powercontroller 205, the transmission power of the DRC signal output fromspreading section 204 is adjusted to this obtained transmission power,and a DRC signal that has been subjected to transmission power controlis output to the multiplexer 210. To give a specific example, if thenumber of the DRC signal output from the DRC signal creation section 202to the DRC power controller 205 is 5, the transmission power of the DRCsignal output from spreading section 204 is adjusted to a transmissionpower 2 dB lower than the transmission power of the pilot signal outputfrom the pilot power controller 209.

The DRC signal that has undergone transmission power control ismultiplexed with the pilot signal by the multiplexer 210,frequency-converted to radio frequency by the transmit RF section 211,and transmitted to the base station as a radio signal from the antenna213 via the duplexer 212.

The radio signal transmitted from the communication terminal is receivedby the antenna 111 of the base station, and input to the receive RFsection 112 via the duplexer 110. The signal input to the receive RFsection 112 is frequency-converted to baseband, despread by thedespreading section 113 using the spreading code used to spread the DRCsignal, and output to the demodulator 114 and reception powercalculation section 115.

In the demodulator 114 the output signal from the despreading section113 is demodulated, and the DRC signal is extracted and output to theallocation section 101.

Here, since a DRC signal indicating that downlink channel quality ispoor is transmitted by a communication terminal at lower transmissionpower than in a conventional system, the probability of a DRC signalindicating that downlink channel quality is poor being receivederroneously by the base station is increased. Also, as stated above, ifcommunication resource allocation is performed based on an erroneouslyreceived DRC signal, downlink throughput will fall.

Thus, in the reception power calculation section 115, the receptionpower of the despread DRC signal is measured, and is output to theunused DRC detection section 116. The lowest reception power at which anerror does not occur in a DRC signal indicating that downlink channelquality is poorest (a DRC signal with DRC number 1 in FIG. 4) has beenset beforehand in the unused DRC detection section 116 as a thresholdvalue. Then, in the unused DRC detection section 116, a DRC signal ofreception power lower than this threshold value is detected, and thedetection result is output to the allocation section 101. A DRC signaldetected by the unused DRC detection section 116 is a DRC signal that isnot used by the allocation section 101 in determining communicationresource allocation.

In the allocation section 101, communication resource allocation to eachcommunication terminal is determined based on the DRC signals remainingafter DRC signals detected by the unused DRC detection section 116 havebeen excluded from the DRC signals extracted by the demodulator 114.

Thus, in a base station according to this embodiment, a DRC signal ofreception power lower than the lowest reception power at which a DRCsignal indicating that downlink channel quality is poorest is notreceived erroneously is excluded. That is to say, in abase stationaccording to this embodiment, a notification signal susceptible toerrors is excluded in determining downlink communication resourceallocation. Therefore, according to a base station of this embodiment,even though a DRC signal indicating that downlink channel quality ispoor is transmitted at lower transmission power than in a conventionalsystem, it is possible to prevent communication resource allocation frombeing determined based on an erroneous DRC signal.

Thus, according to this embodiment, the better the downlink channelquality indicated by a DRC signal, the higher is the transmission powerat which transmission is performed, and therefore it is possible to makeDRC signals indicating that downlink channel quality is goodproportionally less susceptible to errors, and to reduce the erroroccurrence rate of DRC signals for which the probability of selection bya base station is high. By this means it is possible to reduce thepossibility of communication resource allocation being determined basedon an erroneous DRC signal, and so to prevent a fall in downlinkthroughput.

A base station according to this embodiment may also be configured asshown in FIG. 5. FIG. 5 is a block diagram showing another configurationof a base station according to Embodiment 1 of the present invention.That is to say, a base station may be configured in such a way that thereception power calculation section 115 and unused DRC detection section116 shown in FIG. 2 are replaced by a likelihood calculation section 301and unused DRC detection section 302. In the following description,parts identical to those in FIG. 2 are assigned the same referencenumerals as in FIG. 2 and their detailed explanations are omitted.

In FIG. 5, the likelihood calculation section 301 calculates alikelihood that indicates the probable degree of certainty of a DRCsignal, and outputs the calculation result to the unused DRC detectionsection 302. The lowest likelihood at which an error does not occur in aDRC signal indicating that downlink channel quality is poorest has beenset beforehand in the unused DRC detection section 302 as a thresholdvalue. Then, in the unused DRC detection section 302, a DRC signal witha likelihood lower than this threshold value is detected, and thedetection result is output to the allocation section 101.

In this way the same kind of effect as described above is also obtainedwhen a base station according to this embodiment is configured as shownin FIG. 5.

Embodiment 2

In a communication terminal according to Embodiment 2 of the presentinvention, the better the down link channel quality indicated by a DRCsignal, the larger is the code word minimum distance of the code word towhich that DRC signal is converted with respect to other DRC signal codewords before being transmitted.

FIG. 6 is a block diagram showing the configuration of a communicationterminal according to Embodiment 2 of the present invention. As shown inthis figure, a communication terminal according to this embodiment isconfigured in such away that the modulator 203, spreading section 204,DRC power controller 205, and transmission power table 206 shown in FIG.3 are replaced by a code word selector 401, code word table 402,modulator 403, and spreading section 404. In the following description,parts identical to those in FIG. 3 are assigned the same referencenumerals as in FIG. 3 and their detailed explanations are omitted.

The code word selector 401 refers to the code word table 402, converts aDRC signal created by the DRC signal creation section 202 to apredetermined code word, and outputs the code word to modulator 403.Modulator 403 modulates the code word and outputs it to spreadingsection 404. Spreading section 404 spreads the output signal frommodulator 403 and outputs the resulting signal to a multiplexer 210.

Next, the operation of a communication terminal according to thisembodiment will be described.

First, the contents set in the code word table 402 will be described.FIG. 7 is a drawing showing the contents of the code word table providedin a communication terminal according to Embodiment 2 of the presentinvention.

The code word table 402 shows the correspondence between DRC numbers andcode words after DRC signal conversion, set so that the higher the DRCnumber, the larger is the code word minimum distance of the code word towhich the DRC signal is converted. Here, numbers 1 to 5 are used as DRCnumbers, with a higher number representing a proportionally betterdownlink channel quality. That is to say, in the settings in the codeword table 402, the better the downlink channel quality indicated by aDRC signal, the larger is the code word minimum distance of the codeword to which the DRC signal is converted.

Here, “code word distance” is the number of bits that differ betweencode words, and “code word minimum distance” is the minimum number ofbits by which a particular code word differs with respect to all othercode words. To be specific, the code word for a DRC signal with DRCnumber 5 is “111111111”, and this code word “111111111” differs by aminimum of 6 bits when compared with any of the code words correspondingto DRC signals with DRC numbers 1 to 4. Therefore, the code word minimumdistance of the code word for a DRC signal with DRC number 5 is 6.Similarly, the code word minimum distance of the code word for a DRCsignal with DRC number 4 is 3.

Thus, the code word for a DRC signal with DRC number 5 is less likely tobe mistaken for another code word than the code word for a DRC signalwith DRC number 4. That is to say, the larger code word minimum distanceof a code word, the less likely it is to be mistaken for another codeword.

In the code word selector 401, a DRC signal output from the DRC signalcreation section 202 is converted to a code word set in the code wordtable 402, and output to modulator 403. To give a specific example, ifthe DRC signal output from the DRC signal creation section 202 is anumber 5 DRC signal, it is converted to code word “111111111”.

Following conversion, the code word is modulated by modulator 403 andspread by spreading section 404. The spread code word is multiplexedwith a pilot signal by a multiplexer 210, frequency-converted to radiofrequency by a transmit RF section 211, and transmitted to the basestation as a radio signal from an antenna 213 via a duplexer 212.

Thus, according to this embodiment, the better the downlink channelquality indicated by a DRC signal, the larger is the code word minimumdistance of the code word to which that DRC signal is converted withrespect to other DRC signal code words before being transmitted, andtherefore it is possible to make DRC signals indicating that downlinkchannel quality is good proportionally less susceptible to errors, andto reduce the error occurrence rate of DRC signals for which theprobability of selection by a base station is high. By this means it ispossible to reduce the possibility of communication resource allocationbeing determined based on an erroneous DRC signal, and so to prevent afall in downlink throughput.

Also, according to this embodiment, it is possible to reduce the erroroccurrence rate of DRC signals for which the probability of selection bya base station is high without increasing DRC signal transmission power,thereby making it possible to reduce the possibility of communicationresource allocation being determined based on an erroneous DRC signalwithout increasing communication terminal power consumption.

Moreover, according to this embodiment, it is possible to change thedegree of insusceptibility to errors of code words corresponding to DRCsignals while keeping the code length of code words constant, andtherefore it is not necessary to provide a plurality of demodulationsystems in accordance with different code lengths in a base station,thus enabling the apparatus configuration of a base station to besimplified.

Embodiment 3

A base station according to Embodiment 3 of the present inventiontransmits to a communication terminal a control signal for tablerewriting based on the rate of occurrence of DRC signals that areexcluded when communication resource allocation is determined, and acommunication terminal according to Embodiment 3 of the presentinvention rewrites the contents of a transmission power table or codeword table based on a control signal transmitted from the base station.

FIG. 8 is a block diagram showing the configuration of a base stationaccording to Embodiment 3 of the present invention. As shown in thisfigure, a base station according to this embodiment is configured byfurther providing the configuration shown in FIG. 2 with a detectionrate calculation section 501, control signal creation section 502,modulator 503, and spreading section 504. In the following description,parts identical to those in FIG. 2 are assigned the same referencenumerals as in FIG. 2 and their detailed explanations are omitted.

In FIG. 8, the detection rate calculation section 501 calculates therate of detection by the unused DRC detection section 116 and outputsthe result to the control signal creation section 502. That is to say,the detection rate calculation section 501 calculates the rate ofoccurrence of DRC signals that are excluded when communication resourceallocation is determined. Based on the detection rate, the controlsignal creation section 502 creates a control signal for table rewriting(hereinafter referred to as “table rewrite signal”), which is output tomodulator 503. Modulator 503 modulates the table rewrite signal andoutputs it to spreading section 504. Spreading section 504 spreads theoutput signal from modulator 503 and outputs the resulting signal to themultiplexer 108.

FIG. 9 is a block diagram showing the configuration of a communicationterminal according to Embodiment 3 of the present invention. As shown inthis figure, a communication terminal according to this embodiment isconfigured by further providing the configuration shown in FIG. 3 with adespreading section 601, demodulator 602, and table rewriting section603. In the following description, parts identical to those in FIG. 3are assigned the same reference numerals as in FIG. 3 and their detailedexplanations are omitted.

In FIG. 9, despreading section 601 despreads a baseband signal using thespreading code used to spread the table rewrite signal, and outputs theresulting signal to the demodulator 602. The demodulator 602 demodulatesthe output signal from despreading section 601 and extracts the tablerewrite signal, which is output to the table rewriting section 603. Thetable rewriting section 603 rewrites the contents of the transmissionpower table in accordance with the table rewrite signal.

Next, the procedure for transmission/reception of signals between thebase station shown in FIG. 8 and the communication terminal shown inFIG. 9 will be described.

First, in the detection rate calculation section 501 of the basestation, the detection rate of the unused DRC detection section 116 iscalculated and is output to the control signal creation section 502. Thedetection rate can be calculated, for example, from the number ofdetections in a predetermined time.

A predetermined threshold value for the detection rate has been set inthe control signal creation section 502, and this threshold value iscompared with the detection rate calculated by the detection ratecalculation section 501. If the detection rate calculated by thedetection rate calculation section 501 is greater than or equal to thethreshold value, a table rewrite signal ordering all transmission powervalues set in the transmission power table 206 to be increased iscreated, and is output to modulator 503. That is to say, if the rate ofoccurrence of DRC signals that are excluded when communication resourceallocation is determined is greater than or equal to the predeterminedthreshold value, the control signal creation section 502 creates a tablerewrite signal that orders all DRC signal transmission power values tobe increased simultaneously from their current values.

The table rewrite signal is modulated by modulator 503, spread byspreading section 504, and output to the multiplexer 108. The spreadtable rewrite signal is multiplexed with transmit data and the pilotsignal in the multiplexer 108, frequency-converted to radio frequency bythe transmit RF section 109, and transmitted to communication terminalsas a radio signal from the antenna 111 via the duplexer 110.

The radio signal transmitted from the base station is received by theantenna 213 of the communication terminal, passes through the duplexer212, and is frequency-converted to baseband by the receive RF section214. The baseband signal is despread by despreading section 601 anddemodulated by the demodulator 602, and the table rewrite signal isextracted. The extracted table rewrite signal is output to the tablerewriting section 603.

The contents of the transmission power table 206 are then rewritten bythe table rewriting section 603 in accordance with the table rewritesignal. That is to say, the table rewriting section 603 increases allthe transmission power values set in the transmission power table 206.

In the above description, the configuration is such that the tablerewriting section 603 rewrites the contents of the transmission powertable 206, but this embodiment may also be applied to a communicationterminal according to Embodiment 2, and a configuration may be usedwhereby the table rewriting section 603 rewrites the contents of thecode word table 402 shown in FIG. 6.

In this case, if the detection rate calculated by the detection ratecalculation section 501 is greater than or equal to the threshold value,the control signal creation section 502 of a base station according tothis embodiment creates a table rewrite signal ordering all code wordminimum distances set in the code word table 402 to be increased. Thatis to say, if the rate of occurrence of DRC signals that are excludedwhen communication resource allocation is determined is greater than orequal to the predetermined threshold value, the control signal creationsection 502 creates a table rewrite signal that orders all code wordminimum distances of code words corresponding to DRC signals to beincreased simultaneously from their current values. Then the tablerewriting section 603 rewrites the contents of the code word table 402in accordance with the table rewrite signal. That is to say, the tablerewriting section 603 rewrites the code words set in the code word table402 with code words all of whose code word minimum distances are largerthan at present.

Thus, according to this embodiment, the contents of the transmissionpower table or code word table are rewritten based on the rate ofoccurrence of DRC signals that are excluded when communication resourceallocation is determined. In other words, in this embodiment,transmission power table or code word table contents are rewrittenadaptively in accordance with variations in the communicationenvironment. That is to say, according to this embodiment, when thecommunication environment deteriorates and the rate of occurrence of DRCsignals that are excluded when communication resource allocation isdetermined reaches or exceeds a predetermined threshold value, thetransmission power of each DRC signal is increased, or the code wordminimum distance of the code word corresponding to each DRC signal isincreased, thereby enabling the DRC signal error occurrence rate to beheld down even when the communication environment deteriorates.

In this embodiment, the predetermined detection rate threshold value isdecided upon considering appropriately the environment in which thecommunication system is used.

Moreover, with this embodiment, it is also possible to further set asecond predetermined threshold value in the control signal creationsection 502 to create a table rewrite signal ordering all transmissionpower values set in the transmission power table 206 to be decreasedwhen the detection rate calculated by the detection rate calculationsection 501 falls below this second threshold value. By this means, itis possible to reduce DRC signal transmission power when DRC signalreception quality becomes excessive, thereby enabling communicationterminal power consumption to be decreased.

Furthermore, in this embodiment, table rewriting is performed based onthe rate of detection by the unused DRC detection section 116, but it isalso possible to rewrite a table based on the distribution of DRCsignals used in determining communication resource allocation from amongDRC signals transmitted from mobile stations, so that that distributionis optimized. In this case, the base station shown in FIG. 8 isconfigured with the detection rate calculation section replaced by aused DRC distribution determination section, which determines thedistribution of DRC signals used in communication resource allocationdetermination based on DRC signals output from the demodulator 114 anddetection results output from the unused DRC detection section 116, andoutputs a signal indicating that distribution to the control signalcreation section 502. The control signal creation section 502 thencreates a table rewrite signal based on the signal indicating thedistribution output from the used DRC distribution determinationsection.

Embodiment 4

A communication terminal according to Embodiment 4 of the presentinvention transmits at higher transmission power in proportion to CIRinformation that indicates that downlink channel quality is good. A basestation according to Embodiment 4 of the present invention excludes CIRinformation for which the reception power is lower than a predeterminedthreshold value in performing communication resource allocation.

In above-described Embodiment 1, a communication terminal determines thecommunication mode based on the CIR and transmits a DRC signalcorresponding to that determined communication mode to the base stationat predetermined transmission power, and the base station determinescommunication resource allocation to each communication terminal basedon the DRC signals. DRC signal can be represented with far fewer bitsthan other information indicating downlink channel quality (such as adownlink CIR, for example), and therefore use of a DRC signal has theadvantage of enabling the downlink channel utilization efficiency to beincreased. On the other hand, since a communication terminal must beprovided with a table for communication mode determination, a table forDRC signal creation, and so forth to determine the communication modeand create a DRC signal, there are the disadvantages of increasedcommunication terminal power consumption and apparatus size.

Thus, in this embodiment, a communication terminal transmits CIRinformation to the base station at predetermined transmission power, andthe base station determines the communication mode based on the CIRinformation and then determines communication resource allocation toeach communication terminal. As a result, although there is thedisadvantage of a slight decrease in the uplink channel utilizationefficiency, the fact that communication terminals do not have todetermine the communication mode and create a DRC signal, and do notneed to be provided with a communication mode determination table, DRCsignal creation table, and so forth, offers the major advantage ofenabling communication terminal power consumption and apparatus size tobe reduced. Also, in this embodiment, it is possible for CIR informationfor a plurality of terminals to be compared in the base station, and thecorrect communication mode to be determined with certainty, making thisembodiment particularly useful in cases such as those where it is notpossible for the communication mode to be determined simply from the CIRin each communication terminal.

A base station according to this embodiment and a communication terminalaccording to this embodiment will be described below. FIG. 10 is a blockdiagram showing a configuration of a base station according toEmbodiment 4 of the present invention. In the following description,parts identical to those in FIG. 2 are assigned the same referencenumerals as in FIG. 2 and their detailed explanations are omitted.

In FIG. 10, a demodulator 701 demodulates the output signal from adespreading section 113, and extracts a signal that contains CIRinformation (hereinafter referred to as “CIR signal”), which is outputto an allocation section 704.

A reception power calculation section 702 measures the reception powerof the despread CIR signal, which is output to an unused CIR detectionsection 703. In the unused CIR detection section 703 is set apredetermined threshold value in the same way as in Embodiment 1, and aCIR signal of reception power lower than this threshold value isdetected, and the result of the detection is output to the allocationsection 704.

A despreading section 113, demodulator 701, reception power calculationsection 702, and unused CIR detection section 703 are provided for eachcommunication terminal. From each demodulator 701 a CIR signal for thecorresponding communication terminal is output, and from each unused CIRdetection section 703 a detection result for the correspondingcommunication terminal is output.

The allocation section 704 determines communication resource allocationto each communication terminal based on CIR information indicated by CIRsignals excluding CIR signals detected by the unused CIR detectionsections 703 from among the CIR signals extracted by the demodulators701. Then, based on the determined communication resource allocation,the allocation section 704 notifies a buffer 102 for output of downlinktransmit data, and outputs the CIR information to a communication modedetermination section 705.

Based on the CIR information output from the allocation section 704, thecommunication mode determination section 705 determines thecommunication mode, which indicates a combination of modulation methodand coding method, and outputs a signal indicating this communicationmode to a modulator 706. In addition,based on the determinedcommunication mode, the communication mode determination section 705indicates the downlink transmit data coding method to an adaptive codingsection 103, and indicates the downlink transmit data modulation methodto an adaptive modulator 104. Modulator 706 modulates the signalindicating the communication mode and outputs it to a spreading section707. Spreading section 707 spreads the output signal from modulator 706and outputs the resulting signal to a multiplexer 108.

FIG. 11 is a block diagram showing the configuration of a communicationterminal according to Embodiment 4 of the present invention. In thefollowing description, parts identical to those in FIG. 3 are assignedthe same reference numerals as in FIG. 3 and their detailed explanationsare omitted.

In FIG. 11, a CIR information creation section 801 creates a CIR signalindicating a CIR measured by a CIR measurement section 219, and outputsit to a modulator 802 and CIR information power controller 804.Modulator 802 modulates the CIR signal and outputs it to a spreadingsection 803. Spreading section 803 spreads the output signal frommodulator 802 and outputs the spread signal to the CIR information powercontroller 804. The CIR information power controller 804 refers to atransmission power table 805 that shows the correspondence between CIRlevel and transmission power, and controls the CIR signal transmissionpower based on the transmission power of a pilot signal output from apilot power controller 209, and outputs the CIR signal that hasundergone transmission power control to a multiplexer 210.

A despreading section 807 despreads the baseband signal using thespreading code used to spread the signal indicating the communicationmode, and outputs the despread signal to a communication mode detectionsection 808. The communication mode detection section 808 demodulatesthe output signal from despreading section 807 and detects thecommunication mode. Then, based on the detected communication mode, thecommunication mode detection section 808 indicates the downlink receivedata demodulation method to an adaptive demodulator 216 and indicatesthe downlink receive data decoding method to an adaptive decodingsection 217.

Next, the procedure for transmission/reception of signals between thebase station shown in FIG. 10 and the communication terminal shown inFIG. 11 will be described.

First, in the communication terminal shown in FIG. 11, the CIR of thepilot signal output from despreading section 218 is measured by the CIRmeasurement section 219, and a CIR signal is created by the CIRinformation creation section 801.

The CIR signal is modulated by modulator 802, spread by spreadingsection 803, and output to the CIR information power controller 804. Inthe transmission power table 805, the correspondence between CIR leveland CIR signal transmission power is shown in the same way as inEmbodiment 1, set so that the CIR signal transmission power increases inproportion to the level of the CIR. That is to say, in the settings intransmission power table 805, as in Embodiment 1, the better thedownlink channel quality indicated by a CIR signal, the higher is thetransmission power. Also, as in Embodiment 1, the CIR signaltransmission power values set in the transmission power table 805 areexpressed as a ratio to the pilot signal transmission power.

In the CIR information power controller 804, the CIR signal transmissionpower is obtained by having the transmission power of the pilot signaloutput from the pilot power controller 209 adjusted in accordance withthe ratios set in the transmission power table 805. Then, in the CIRinformation power controller 804, the transmission power of the CIRsignal output from spreading section 803 is adjusted to this obtainedtransmission power, and a CIR signal that has been subjected totransmission power control is output to the multiplexer 210.

The CIR signal that has under gone transmission power control ismultiplexed with the pilot signal by the multiplexer 210,frequency-converted to radio frequency by a transmit RF section 211, andtransmitted to the base station as a radio signal from an antenna 213via a duplexer 212.

In the base station shown in FIG. 10, the output signal from thedespreading section 113 is demodulated by demodulator 701, and thedemodulated CIR signal is extracted and output to the allocation section704. In the reception power calculation section 702, the reception powerof the despread CIR signal is measured, and is output to the unused CIRdetection section 703. The lowest reception power at which an error doesnot occur in a CIR signal indicating that downlink channel quality ispoorest has been set beforehand in the unused CIR detection section 703as a threshold value, as in Embodiment 1. Then, in the unused CIRdetection section 703, a CIR signal of reception power lower than thisthreshold value is detected, and the detection result is output to theallocation section 704. A CIR signal detected by the unused CIRdetection section 703 is a CIR signal that is not used by the allocationsection 704 in determining communication resource allocation.

In the allocation section 704, communication resource allocation to eachcommunication terminal is determined based on the CIR shown by CIRsignals remaining after CIR signals detected by the unused CIR detectionsection 703 have been excluded from the CIR signals extracted by thedemodulator 701, and CIR information is output to the communication modedetermination section 705.

In the communication mode determination section 705, the communicationmode is determined based on CIR information output from the allocationsection 704, and a signal indicating this communication mode is outputto modulator 706. The signal indicating the communication mode ismodulated by modulator 706, spread by spreading section 707, multiplexedwith transmit data and the pilot signal in the multiplexer 108,frequency-converted to radio frequency by the transmit RF section 109,and transmitted to the communication terminal as a radio signal from anantenna 111 via a duplexer 110.

In the communication terminal shown in FIG. 11, a baseband signal isdespread by despreading section 807, and the despread signal is outputto the communication mode detection section 808. In the communicationmode detection section 808, the output signal from despreading section807 is demodulated and the communication mode is detected, and based onthe detected communication mode, the downlink receive data demodulationmethod is indicated to the adaptive demodulator 216 and the downlinkreceive data decoding method is indicated to the adaptive decodingsection 217.

Thus, according to this embodiment, as in Embodiment 1, the better thedownlink channel quality indicated by a CIR signal, the higher is thetransmission power at which transmission is performed, and therefore itis possible to reduce the error occurrence rate of CIR information forwhich the probability of use by a base station is high. By this means itis possible to reduce the possibility of communication resourceallocation being determined based on erroneous CIR information, and soto prevent a fall in downlink throughput.

Also, according to this embodiment, as in Embodiment 1, a CRI signal ofreception power lower than the lowest reception power at which a CIRsignal indicating that downlink channel quality is poorest is notreceived erroneously is excluded, and therefore, even though a CIRsignal indicating that downlink channel quality is poor is transmittedat lower transmission power than in a conventional system, it ispossible to prevent communication resource allocation from beingdetermined based on erroneous CIR information.

A base station according to this embodiment may also be configured asshown in FIG. 12. FIG. 12 is a block diagram showing anotherconfiguration of a base station according to Embodiment 4 of the presentinvention. That is to say, a base station may be configured in such away that the reception power calculation section 702 and unused CIRdetection section 703 shown in FIG. 10 are replaced by a likelihoodcalculation section 901 and unused CIR detection section 902. In thefollowing description, parts identical to those in FIG. 10 are assignedthe same reference numerals as in FIG. 10 and their detailedexplanations are omitted.

In FIG. 12, the likelihood calculation section 901 calculates alikelihood that indicates the probable degree of certainty of a CRIsignal, and outputs the calculation result to the unused CIR detectionsection 902. The lowest likelihood at which an error does not occur in aCIR signal indicating that downlink channel quality is poorest has beenset beforehand in the unused CIR detection section 902 as a thresholdvalue. Then, in the unused CIR detection section 902, a CIR signal witha likelihood lower than this threshold value is detected, and thedetection result is output to the allocation section 704.

In this way the same effect as described above is also obtained when abase station according to this embodiment is configured as shown in FIG.12.

Embodiment 5

In a communication terminal according to Embodiment 5 of the presentinvention, the better the downlink channel quality indicated by a CIRsignal, the larger is the code word minimum distance of the code word towhich that CIR signal is converted with respect to other CIR signal codewords before being transmitted.

FIG. 13 is a block diagram showing the configuration of a communicationterminal according to Embodiment 5 of the present invention. As shown inthis figure, a communication terminal according to this embodiment isconfigured in such away that the modulator 802, spreading section 803,CIR information power controller 804, and transmission power table 805shown in FIG. 11 are replaced by a code word selector 1001, code wordtable 1002, modulator 1003, and spreading section 1004. In the followingdescription, parts identical to those in FIG. 11 are assigned the samereference numerals as in FIG. 11 and their detailed explanations areomitted.

The code word selector 1001 refers to the code word table 1002, convertsa CIR signal created by the CIR information creation section 801 to apredetermined code word, and outputs it to modulator 1003. Modulator1003 modulates the code word and outputs it to spreading section 1004.Spreading section 1004 spreads the output signal from modulator 1003 andoutputs the resulting signal to a multiplexer 210.

Next, the operation of a communication terminal according to thisembodiment will be described.

In the same way as in above-described Embodiment 2, the code word table1002 shows the correspondence between CIR level and code words after CIRsignal conversion, set so that the higher the CIR level, the larger isthe code word minimum distance of the code word to which the CIR signalis converted. That is to say, in the settings in the code word table1002, the better the downlink channel quality indicated by a CIR signal,the larger is the code word minimum distance of the code word to whichthe CIR signal is converted.

In the code word selector 1001, a CIR signal output from the CIRinformation creation section 801 is converted to a code word set in thecode word table 1002, and output to modulator 1003. Followingconversion, the code word is modulated by modulator 1003 and spread byspreading section 1004. The spread code word is multiplexed with a pilotsignal by a multiplexer 210, frequency-converted to radio frequency by atransmit RF section 211, and transmitted to the base station as a radiosignal from an antenna 213 via a duplexer 212.

Thus, according to this embodiment, as in Embodiment 2, the better thedownlink channel quality indicated by a CIR signal, the larger is thecode word minimum distance of the code word to which that CIR signal isconverted with respect to other CIR signal code words before beingtransmitted, and therefore it is possible to reduce the error occurrencerate of CIR information for which the probability of use by a basestation is high. By this means it is possible to reduce the possibilityof communication resource allocation being determined based on erroneousCIR information, and so to prevent a fall in downlink throughput.

Also, according to this embodiment, as in Embodiment 2, it is possibleto reduce the error occurrence rate of CIR information for which theprobability of use by a base station is high without increasing CIRsignal transmission power, thereby making it possible to reduce thepossibility of communication resource allocation being determined basedon erroneous CIR information without increasing communication terminalpower consumption.

Moreover, according to this embodiment, as in Embodiment 2, it ispossible to change the degree of insusceptibility to errors of codewords corresponding to CIR signals while keeping the code length of codewords constant, and therefore it is not necessary to provide a pluralityof demodulation systems in accordance with different code lengths in abase station, thus enabling the apparatus configuration of a basestation to be simplified.

Embodiment 6

A communication terminal according to Embodiments 6 to 8 of the presentinvention transmits with less susceptibility to errors in thepropagation path in proportion to information for which the amount ofchange is large within CIR information. In other words, a communicationterminal according to Embodiments 6 to 8 of the present inventiontransmits with less susceptibility to errors in the propagation path inproportion to information that indicates a broad value within CIRinformation.

The meaning of “information for which the amount of change is large” and“information that indicates a broad value” here can be illustrated by aspecific example. If a CIR value is indicated by a value with a decimalfraction (such as 8.7 dB), then the above-mentioned information refersto the integer part (here, “8”). In this case, since the amount ofchange per unit of the integer part is 1 dB, while the amount of changeper unit of the fractional part is 0.1 dB, the integer part is“information for which the amount of change is large”. Therefore, if aninteger part is received erroneously by a base station, the degree oferror is large compared with the case where a fractional part isreceived erroneously, and the probability of an erroneous communicationmode being determined is higher-that is to say, the probability ofdownlink throughput falling is higher.

Also, CIR information is normally converted to a code word with alimited number of bits before being transmitted to a base station, andthere are also limits on the transmission power and spreading codespreading factor that can be used in transmitting CIR information. Thereare thus limits to making CIR information overall insusceptible toerrors, and it is difficult to do so.

Thus, in Embodiments 6 to 8 of the present invention, within theabove-described limitations on transmission of CIR information,transmission is performed with insusceptibility to errors in thepropagation path made proportional to “information for which the amountof change is large” within the above limitations so that, at least“information for which the amount of change is large” (that is,“information that indicates a broad value”) of CIR information isreceived correctly.

A communication terminal according to Embodiment 6 of the presentinvention is described below. A communication terminal according toEmbodiment 6 of the present invention performs conversion to, andtransmits, a code word with a code length proportional to the value ofthe upper digit in a CIR value.

FIG. 14 is a block diagram showing the configuration of a communicationterminal according to Embodiment 6 of the present invention. In thefollowing description, parts identical to those in FIG. 11 are assignedthe same reference numerals as in FIG. 11 and their detailedexplanations are omitted.

In FIG. 14, a CIR signal creation section 1101 converts a CIR valuemeasured by a CIR measurement section 219 to a code word and creates aCIR signal, and outputs the created CIR signal to amultiplexer 210. Atthis time, the CIR signal creation section 1101 creates a CIR signal byperforming conversion to a code word with a code length proportional tothe value of the upper digit in the CIR value.

Next, the configuration of the CIR signal creation section 1101 will bedescribed. FIG. 15 is a block diagram showing the configuration of theCIR signal creation section of a communication terminal according toEmbodiment 6 of the present invention.

In FIG. 15, an upper digit information generation section 1201 outputsthe value of the upper digit in the CIR value output from the CIRmeasurement section 219 to a 6-bit coding section 1203. A lower digitinformation generation section 1202 outputs the value of the lower digitin the CIR value output from the CIR measurement section 219 to a 4-bitcoding section 1204. To give a specific example, if the CIR value outputfrom the CIR measurement section 219 is 8.7 dB, the upper digitinformation generation section 1201 outputs the value of the integerpart, “8”, to the 6-bit coding section 1203, and the lower digitinformation generation section 1202 outputs the value of the fractionalpart, “7”, to the 4-bit coding section 1204.

The 6-bit coding section 1203 converts the value output from the upperdigit information generation section 1201 (here, “8”) to a 6-bit codeword, and outputs the 6-bit code word to a time multiplexer 1205. The4-bit coding section 1204 converts the value output from the lower digitinformation generation section 1202 (here, “7”) to a 4-bit code word,and outputs the 4-bit code word to the time multiplexer 1205. It isherein assumed that the number of bits that can be used to indicate aCIR value is ten.

The time multiplexer 1205, by storing the 6-bit code word in the firsthalf of a slot and storing the 4-bit code word in the following latterhalf of the slot, performs time multiplexing of the code word for theinteger part of the CIR value (that is, the code word corresponding tothe value of the upper digit) and the code word for the fractional partof the CIR value (that is, the code word corresponding to the value ofthe lower digit). The time multiplexer 1205 then outputs thetime-multiplexed 10-bit code word to a modulator 1206 as a CIR signal.It is herein assumed that one slot is composed of 10 bits, with theinteger part of a CIR value represented by the preceding 6 bits and thefractional part of a CIR value represented by the succeeding 4 bits.

The modulator 1206 modulates the CIR signal and outputs it to thespreading section 1207. The spreading section 1207 spreads the outputsignal from the modulator 1206 and outputs the resulting signal to themultiplexer 210.

Next, the operation of a communication terminal with the aboveconfiguration will be described.

In the 6-bit coding section 1203, the value of the upper digit in theCIR value (here, “8”) is converted to a 6-bit code word, and the valueof the lower digit in the CIR value (here, “7”) is converted to a 4-bitcode word.

As the number of different code words that can be represented by 6 bitsis 2⁶, and the number of different code words that can be represented by4 bits is 2⁴, the code word minimum distance between code words can bemade larger for code words represented by 6 bits. Therefore, a code wordrepresented by 6 bits is less susceptible to being mistaken for anothercode word than a code word represented by 4 bits. That is to say, inthis embodiment, the value of the upper digit of a CIR value is lesssusceptible to errors.

Thus, with a communication terminal according to this embodiment, withinthe limitation of 10 bits available to indicate a CIR value, byperforming conversion to a code word of a code length proportional tothe value of the upper digit in a CIR value, it is possible to performtransmission with insusceptibility to errors made proportional to thevalue of the upper digit for which the amount of change is large. Bythis means, even if an error should occur in a CIR signal in thepropagation path, the probability of being able to perform receptioncorrectly at the base station is proportionally higher according to thevalue of the upper digit in a CIR value, and the degree of error in CIRvalues can be kept low. Thus, it is possible to reduce the possibilityof an erroneous communication mode being determined in the base station.

In this embodiment, a case has been described where the upper digitvalue is converted to a 6-bit code word and the lower digit value isconverted to a 4-bit code word. However, as long as the number of bitsof the code word corresponding to the upper digit value is greater thanthe number of bits of the code word corresponding to the lower digitvalue, there are no particular limitations on these numbers of bits.

Embodiment 7

A communication terminal according to Embodiment 7 of the presentinvention transmits with transmission power increased in proportion tothe value of the upper digit in a CIR value.

A communication terminal according to this embodiment differs from acommunication terminal according to Embodiment 6 only in the internalconfiguration of the CIR signal creation section 1101, and thereforeonly the CIR signal creation section 1101 will be described in thefollowing description.

FIG. 16 is a block diagram showing the configuration of the CIR signalcreation section of a communication terminal according to Embodiment 7of the present invention. In the following description, parts identicalto those in FIG. 15 are assigned the same reference numerals as in FIG.15 and their detailed explanations are omitted.

The CIR signal creation section 1101 shown in FIG. 16 converts a CIRvalue measured by a CIR measurement section 219 to a code word, and thencreates a CIR signal, increasing transmission power in proportion to thevalue of the upper digit.

In FIG. 16, a 5-bit coding section 1301 converts the value output froman upper digit information generation section 1201 to a 5-bit code wordand outputs the 5-bit code word to a modulator 1303, and a 5-bit codingsection 1302 converts the value output from a lower digit informationgeneration section 1202 to a 5-bit code word and outputs the 5-bit codeword to a modulator 1304. Thus, in this embodiment, both the upper digitvalue and the lower digit value are converted to 5-bit code words, andtherefore there is no difference between them in insusceptibility toerrors from a code word standpoint.

Modulator 1303 modulates the code word output from 5-bit coding section1301, and outputs it to an upper digit spreading section 1305. Modulator1304 modulates the code word output from 5-bit coding section 1302, andoutputs it to a lower digit spreading section 1306.

The upper digit spreading section 1305 spreads the output signal frommodulator 1303, and outputs the spread signal to an upper digit powercontroller 1307. The lower digit spreading section 1306 spreads theoutput signal from modulator 1304, and outputs the spread signal to alower digit power controller 1308. At this time, the upper digitspreading section 1305 and lower digit spreading section 1306 performtheir respective spreading processing using different spreading codes ofthe same spreading factor. That is to say, the upper digit value of theCIR value and the lower digit value of the CIR value are spread usingdifferent spreading codes that have the same spreading factor.

Based on the transmission power of a pilot signal output from a pilotpower controller 209, the upper digit power controller 1307 controls thetransmission power of the signal indicating the upper digit value of theCIR value, and outputs the signal that has undergone transmission powercontrol to a code multiplexer 1309. Similarly, based on the transmissionpower of the pilot signal output from the pilot power controller 209,the lower digit power controller 1308 controls the transmission power ofthe signal indicating the lower digit value of the CIR value, andoutputs the signal that has undergone transmission power control to thecode multiplexer 1309. The actual transmission power control method willbe described later herein.

The code multiplexer 1309 multiplexes the signal indicating the upperdigit value of the CIR value and the signal indicating the lower digitvalue of the CIR value in the same time slot. That is to say, the codemultiplexer 1309 performs code multiplexing of the signal indicating theupper digit value and the signal indicating the lower digit value.

Next, the operation of a communication terminal with the aboveconfiguration will be described.

In the upper digit power controller 1307, a signal indicating the upperdigit value of a CIR value is adjusted to a transmission power whoseonly predetermined value is higher than the pilot signal transmissionpower. In the lower digit power controller 1308, a signal indicating thelower digit value of the CIR value is adjusted to a transmission powerwhose only predetermined value is lower than the pilot signaltransmission power. That is to say, the transmission power is increasedin proportion to the value of the upper digit in the CIR value.

Thus, a communication terminal according to this embodiment can transmitwith insusceptibility to errors made proportional to the upper digitvalue for which the amount of change is large by transmitting withtransmission power increased in proportion to the upper digit value of aCIR value. By this means, even if an error should occur in a CIR signalin the propagation path, the probability of being able to performreception correctly at the base station is proportionally higheraccording to the value of the upper digit in a CIR value, and the degreeof error in CIR values can be kept low. Thus, it is possible to reducethe possibility of an erroneous communication mode being determined inthe base station.

Also, in this embodiment, by increasing transmission power of the upperdigit value compared with conventional CIR signal transmission power(here, the pilot signal transmission power), and decreasing transmissionpower of the lower digit value by the amount by which it is increasedfor the upper digit value, giving a total transmission powerincrease/decrease value of ±0 dB, the overall CIR signal transmissionpower is kept the same as conventional CIR signal transmission power.Thus, according to this embodiment, it is possible to performtransmission within susceptibility to errors made proportional to theupper digit value while keeping CIR signal transmission power the sameas in a conventional system. That is to say, it is possible to performtransmission with insusceptibility to errors made proportional to theupper digit value without reducing uplink capacity compared with aconventional system.

Embodiment 8

A communication terminal according to Embodiment 8 of the presentinvention transmits with spreading performed using a spreading code witha higher spreading factor in proportion to the value of the upper digitin a CIR value.

A communication terminal according to this embodiment differs from acommunication terminal according to Embodiment 6 or 7 only in theinternal configuration of the CIR signal creation section 1101, andtherefore only the CIR signal creation section 1101 will be described inthe following description.

FIG. 17 is a block diagram showing the configuration of the CIR signalcreation section of a communication terminal according to Embodiment 8of the present invention. In the following description, parts identicalto those in FIG. 15 or FIG. 16 are assigned the same reference numeralsas in FIG. 15 or FIG. 16 and their detailed explanations are omitted.

The CIR signal creation section 1101 shown in FIG. 17 converts a CIRvalue measured by a CIR measurement section 219 to a code word, and thencreates a CIR signal, with spreading performed using a spreading codewith a higher spreading factor in proportion to the value of the upperdigit.

In FIG. 17, an upper digit spreading section 1401 spreads the outputsignal from modulator 1303 and outputs the resulting signal to a timemultiplexer 1205, and a lower digit spreading section 1402 spreads theoutput signal from modulator 1304 and outputs the spread signal to thetime multiplexer 1205. At this time, the upper digit spreading section1401 performs spreading processing with a spreading code of the samekind as used by the lower digit spreading section 1402 and with a higherspreading factor than that of the lower digit spreading section 1402.That is to say, the upper digit value of the CIR value is spread with ahigher spreading factor than the lower digit value. As a result,insusceptibility to errors in the propagation path is proportional tothe upper digit value.

Thus, a communication terminal according to this embodiment can transmitwith insusceptibility to errors made proportional to the upper digitvalue for which the amount of change is large by transmitting withspreading performed using a spreading code with a higher spreadingfactor in proportion to the value of the upper digit in a CIR value. Bythis means, even if an error should occur in a CIR signal in thepropagation path, the probability of being able to perform receptioncorrectly at the base station is proportionally higher according to thevalue of the upper digit in a CIR value, and the degree of error in CIRvalues can be kept low. Thus, it is possible to reduce the possibilityof an erroneous communication mode being determined in the base station.

Also, in this embodiment, the spreading factor for the upper digit valueis increased compared with a conventional CIR signal spreading factor,and the spreading factor for the lower digit value is decreased by theamount by which it is increased for the upper digit value. By thismeans, the amount of data sent in one slot is kept the same as for aconventional CIR signal. Thus, according to this embodiment, it ispossible to perform transmission with insusceptibility to errors madeproportional to the upper digit value without reducing the amount ofdata sent in one slot.

It is also possible to implement the present invention by combining acommunication terminal according to above-described Embodiment 1 and acommunication terminal according to above-described Embodiment 2.Moreover, it is also possible to implement the present invention bycombining a communication terminal according to above-describedEmbodiment 4 and a communication terminal according to above-describedEmbodiment 5. Furthermore, it is also possible to implement the presentinvention by combining the respective communication terminals accordingto above-described Embodiments 6 to 8. In addition, it is also possiblefor the transmission power table provided in a communication terminalaccording to above-described Embodiment 4 and the code word tableprovided in a communication terminal according to above-describedEmbodiment 5 to be rewritten as appropriate based on a control signalfrom the base station, in the same way as in above-described Embodiment3.

Also, in above-described Embodiments 1 to 8, a case has been describedwhere a pilot signal is time-multiplexed, but above-describedEmbodiments 1 to 8 are not limited to this, and can also be applied to acase where a pilot signal is code-multiplexed.

Moreover, in above-described Embodiments 1 to 8, a CIR has been used asa value that indicates pilot signal reception quality, but this is not alimitation, and any value may be used as long as it is a value thatindicates reception quality.

Furthermore, in above-described Embodiments 1 to 5, the predeterminedthreshold value set in the unused DRC detection section or the unusedCIR detection section is assumed to be a fixed value, but aconfiguration may also be used whereby the threshold value is variedadaptively in accordance with the DRC signal error rate or CIR signalerror rate.

In addition, in above-described Embodiments 6 to 8, either timemultiplexing or code multiplexing may be used when multiplexing codewords.

Also, in above-described Embodiments 6 to 8, an example has been givenin which a CIR value is represented by one integer-part digit and onefractional-part digit. However, this is not a limitation, andabove-described Embodiments 6 to 8 may all be implemented for CIR valuesrepresented by a plurality of digits.

Moreover, in above-described Embodiments 6 to 8, the value of the upperdigit of a CIR value has been described as “information for which theamount of change is large”. However, “information for which the amountof change is large” does not necessarily correspond to the size of adigit. For example, if a method is used whereby a CIR value isrepresented by an integer by first indicating a broad value of 0 db,2dB, 4 dB, 6 dB . . . changing by 2 dB at a time, and adding informationindicating the presence or absence of an increment of 1 dB for thatbroad value, a value changing by 2 dB at a time is “information forwhich the amount of change is large”. With this method, to represent aCIR value of 7 dB, for example, CIR information that includesinformation indicating 6 dB and information indicating that there is anincrement of 1 dB is transmitted to the base station. At this time, thecommunication terminal apparatus transmits the information indicating 6dB with greater insusceptibility to errors than the informationindicating that there is an increment of 1 dB, in the same way as inabove-described Embodiments 6 to 8.

As described above, according to the present invention it is possible toprevent a fall in downlink throughput in a communication system in whichcommunication resources are allocated to communication terminals basedon downlink channel quality.

This application is based on Japanese Patent Application No. 2000-234420filed on Aug. 2, 2000, and Japanese Patent Application No. 2000-285405filed on Sep. 20, 2000, entire content of which is expresslyincorporated by reference herein.

What is claimed is:
 1. A communication terminal apparatus comprising: ameasurer that measures a downlink channel quality and outputsinformation that is generated in association with said downlink channelquality and composed of a plurality of digits including an upper digitand a lower digit; a coder that encodes the information such that theupper digit has a larger code word minimum distance than the lowerdigit; and a transmitter that transmits the encoded information to abase station apparatus.
 2. The communication terminal apparatusaccording to claim 1, wherein the upper digit contains a mostsignificant bit of the information.
 3. A communication terminalapparatus comprising: a measurer that measures a downlink channelquality and outputs information that is generated in association withsaid downlink channel quality and composed of a plurality of digitsincluding an upper digit and an lower digit; a coder that encodes theinformation such that the upper digit is assigned a larger number ofbits than the lower digit; and a transmitter that transmits the encodedinformation to a base station apparatus.
 4. The communication terminalapparatus according to claim 3, wherein the upper digit contains a mostsignificant bit of the information.
 5. A coding and transmission methodfor use in a communication system where a base station apparatus assignsa downlink channel to each of a plurality of communication terminalapparatuses on a time division basis, wherein said each of a pluralityof communication terminal apparatuses: encodes information that is usedfor the assignment of the downlink channel and composed of a pluralityof digits including an upper digit and a lower digit such that the upperdigit has a larger code word minimum distance than the lower digit; andtransmits the encoded information to said base station apparatus.
 6. Thecoding and transmission method according to claim 5, wherein the upperdigit contains a most significant bit of the information.
 7. A codingand transmission method for use in a communication system where a basestation apparatus assigns a downlink channel to each of a plurality ofcommunication terminal apparatuses on a time division basis, whereinsaid each of a plurality of communication terminal apparatuses: encodesinformation that is used for the assignment of the downlink channel andcomposed of a plurality of digits including an upper digit and a lowerdigit such that the upper digit is assigned a larger number of bits thanthe lower digit; and transmits the encoded information to said basestation apparatus.
 8. The coding and transmission method according toclaim 7, wherein the upper digit contains a most significant bit of theinformation.